The present invention relates to a method and an apparatus for preventing pulsation generated in a fluid (particularly a liquid) when the fluid is pressure-fed through piping or the like, and particularly relates to a method for preventing pulsation of fluid generated in the case where liquid is pressure-fed by means of a pump, which is apt to generate pulsation, such as a diaphragm pump, a plunger pump, a gear pump, or the like.
Generally, a pressure-feeding pump, which is apt to generate pulsation, has been Widely used When a gas or a liquid such as paint, photosensitive coating liquid, or the like is pressure-fed from a source to its destination (e.g. an apparatus for painting) through a pipe or the like.
If pulsation of pressure-fed fluid is sufficiently extreme or violent, the feeding of the fluid becomes discontinuous, making volume regulation difficult, if not impossible. In addition, the variations in pressure due to the pulsation can cause an over-load on and damage the feeding pump.
Moreover, where the fluid is a photosensitive coating liquid being pressure-fed to a coating apparatus (for application to a material), if pulsation occurs, uniformly coated products cannot be obtained, and the coating liquid cannot achieve its function as a photosensitive material. In addition, in a painting process, discharge of the paint or the like becomes uneven or discontinuous making it extremely difficult to paint uniformly.
Accordingly, when feeding fluid through piping using a pump, it is necessary to eliminate as much of the pulsation as possible.
Conventionally, in a method of preventing or reducing pulsation, a closed hollow chamber is communicated with a portion of a pipe connecting a pressure-feeding portion of a pressure-feeding pump or the like to a portion of destination so that the pulsation generated in pressure feeding the liquid can be absorbed as compression/expansion of air in the hollow chamber. The hollow chamber is in a closed state except that the inside of the chamber is communicated with the pipe, and the air pressure inside the chamber is increased beyond atmospheric pressure in pressure-feeding the liquid because the air is pressured into the hollow chamber at that time. Relating to this method, various inventions are disclosed, for example, in Japanese Patent Unexamined Publication Nos. 56-160497 and 58-217890 and Japanese Utility Model Unexamined Publication No. 59-73692.
However, it has been found that pulsation preventing methods have various drawbacks.
In the method in which the closed hollow chamber is communicated with the feeding pipe, the degree of pulsation varies remarkably depending on conditions such as the kind of pump, the feed pressure, the feed quantity, the characteristics of the fluid, the material and inner diameter of the pipe, etc. However, it is necessary to determine the size of the hollow chamber in accordance with the degree of the pulsation. That is, it is necessary to make the volume of the chamber larger as the pulsation becomes larger. Accordingly, the size of the hollow chamber is designed on the basis of the foregoing conditions. It is therefore necessary to prepare chambers having various inside volumes. Accordingly, the manufacturing costs and labor are extremely large.
Further, if the degree of pulsation is large, and the liquid is expensive or may change in conditions with time, such as a photosensitive coating liquid, it is necessary to use a hollow chamber having a large volume to prevent pulsation. As a result, a larger amount of liquid flows into the chamber in pressure feeding, which increases the amount of waste, because any excess liquid is exhausted after completion of the pressure feeding.
In order to improve the foregoing defects, Japanese Patent Unexamined Publication No. 56-160497 discloses a method in which a liquid is pressure-fed after the air pressure inside a hollow chamber has been made higher than atmospheric pressure.
Such a method is disadvantageous in that a liquid which has been subjected to treatment for removal of a dissolved gas (e.g. dissolved air by deaeration treatment), if the liquid is pressure-fed in the hollow chamber for a long time, the deaeration-treated liquid absorbs air so that not only the effect of the deaeration treatment is counteracted, but also the amount of the liquid flowing into the holloW chamber increases.
The pulsation preventing method using such a hollow chamber has a further disadvantage that it requires much labor and time to clean the chamber when a new liquid to be pressure-fed is to be used.
In place of the pulsation preventing method using such a hollow chamber having various disadvantages as described above, Japanese Patent Unexamined Publication No. 58-217890 and Japanese Utility Model Unexamined Publication No. 59-73692 disclose pulsation preventing methods using elastic tubes which are able to expand/contract axially.
The foregoing pulsation preventing methods using such elastic tubes are disadvantageous in that when an organic solvent, a photosensitive coating liquid using an organic solvent as a solvent, or an aqueous photosensitive coating liquid including an organic solvent, are used, the elastic tubes swell with or are dissolved in the organic solvent to thereby lose their characteristics, so that it sometimes becomes difficult if not impossible to achieve the pulsation preventing effect.
It has therefore been required to provide elastic tubes which are proven to withstand an organic solvent. At present, however, there are no known inexpensive elastic tubes which are useful for any kind of organic solvents. Further, although there is an elastic tube made of a material which is proven against a certain kind of organic solvent, such an elastic tube is so expensive and therefore very disadvantageous from an economical point of view.